The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for supporting broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. The IEEE 802.16a standard was approved in 2003. In the IEEE 802.16a standard, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ are further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 (hereinafter, IEEE 802.16e) was completed in 2005 in a format of ‘corrigendum’.
Recently, standardization on the IEEE 802.16m is in progress as a new technical standard based on the IEEE 802.16e. The IEEE 802.16m, which is a newly developed technical standard, has to be designed to support the previously designed IEEE 802.16e. That is, a technology (i.e., IEEE 802.16m) of a newly designed system has to be configured to operate by effectively incorporating a conventional technology (i.e., IEEE 802.16e). This is called backward compatibility. The backward compatibility considered in the design of IEEE 802.16m is as follows.
First, a new user equipment (UE) employing a new technology has to operate with the same performance as a legacy UE employing a conventional technology with a legacy base station (BS). Second, a new system has to operate in the same radio frequency (RF) subcarrier and the same bandwidth as those of a legacy system. Third, a new BS has to support a case where a new UE and a legacy UE coexist in the same RF subcarrier, and overall system performance has to be improved by a ratio of the new UE. Fourth, a new BS has to support a handover of a legacy UE and a handover of the new UE such that their handover performances conform to those of legacy BSs. Fifth, a new BS has to support both a UE and a legacy UE to the same level as that supported by a legacy BS to the legacy UE.
A BS performs scheduling to allocate radio resources to a UE. The scheduling is performed in a medium access control (MAC) layer which is an upper layer of a physical layer for transmitting data through a radio channel. A transmission time interval (TTI) is a basic unit of scheduling performed in the MAC layer. The TTI may be a unit of radio resource allocation. Control information on radio resource allocation can be transmitted together for each TTI transmitted in the physical layer. In general, a TTI size is determined by considering a size of transmission data, a data transmission latency in hybrid automatic repeat request (HARQ), an overhead caused by control information, etc. For example, if the TTI size is set to be less than a data transfer block, a transfer block segmentation process has to be performed in the MAC layer, which results in an overhead in performance of the MAC layer. In addition, latency and complexity may increase in a transmission process since the data transfer block is transmitted through a plurality of TTIs. On the other hand, if the TTI size is set to be significantly larger than the data transfer block, the number of data transfer blocks to be multiplexed to one TTI increases. Accordingly, control information is additionally required for the multiplexed data transfer block, thereby increasing an overhead caused by the control information.
When the TTI size is fixed to one size with respect to various-sized data, a problem may arise in that latency and complexity increase in the transmission process or an overhead caused by the control information increases. For example, a normal data packet of internet Protocol (IP) traffic has a size of approximately 500 bytes, and a voice packet of a voice over IP (VoIP) service has a size of approximately 30 to 40 bytes. In addition, since the IEEE 802.16m system has to provide more various types of data services while satisfying a backward compatibility with the IEEE 802.16e system, the use of the TTI whose size is fixed to one size cannot satisfy the various types of data services.
Accordingly, there is a need for a method capable of adaptively employing a TTI to satisfy various types of data services.